Generally, an air conditioner is an appliance which cools or heats an indoor space by using a refrigeration cycle of a refrigerant comprising a compressor, a condenser, an expansion device and an evaporator so as to offer a pleasant indoor environment to users.
The air conditioner comprises an evaporator which performs heat exchange between water and a refrigerant, and a heat exchanger such as a chilled water coil in which the water cooled by the heat exchange cools an air, so that the chilled air cooled by the heat exchanger blows to the indoor space and can cool the indoor space.
In the conventional air conditioner, if the air conditioner operates, a compressor is operated, and if the air conditioner stops, the compressor is stopped. When the compressor is operated, the chilled water can cool an air and the air can cool the indoor space. If the temperature of the chilled water is not appropriately changed according to the cooling load of the indoor space, the air conditioner is difficult to operate by optimum efficiency and to respond to the partial load effectively.